Container closures, sealed containers and sealing compositions for them

ABSTRACT

A sealing composition for a container closure comprises a polymeric matrix material and its oxygen permeability is reduced by incorporating ethylene vinyl alcohol polymer into the composition. The composition can be in fluid or meltable form ready for application to a closure or it can be present as a deposit on the closure, for instance a gasket around the closure.

This is a division of application Ser. No. 07/711,845, filed Jun. 7,1991, now U.S. Pat. No. 5,183,848, a division of application Ser. No.07/370,546 filed on Jun. 23, 1989, now abandoned.

This invention relates to materials that can be used to improve theshelf life of packaged materials, such as bottled beer.

It is standard practice to form containers from materials that areimpermeable to oxygen, such as glass or metal, or of very lowpermeability, such as laminated polymeric material including a barrierlayer that may be formed of, for instance, a blend of polypropylene andethylene vinyl alcohol (see for instance EP 142183). It is also knownfrom U.S. Pat. Nos. 3,857,754 and 3,975,463 to form articles such asbottles from certain compositions that include certain saponifiedethylene-vinyl acetate copolymers.

When the container is formed of a glass or metal body and is providedwith a metal closure, then permeation of oxygen or other gas through thebody and the closure is impossible because of the impermeability of thematerials from which the body and closure are formed. However it haslong been recognised that when conventional containers of this type areused for the storage of materials such as beer, the shelf life of thestored materials is very limited due to the ingress of gases. Forinstance the quality of the beer stored in glass bottles having metalcaps tends to deteriorate after storage for a month or so.

Although ingress of oxygen is a main cause of deterioration of beer,off-flavours can also arise when the container is exposed to anatmosphere containing other gases that can give an unpleasant flavour.For instance the containers are sometimes packed on pallets or in cratesmade of wood that has been impregnated with a preservative that mayresult in the atmosphere being contaminated with chloroanisole and it isnecessary to prevent ingress of this.

The most effective way of prolonging the storage life has been toprovide a gasket of cork and aluminium foil between the closure and thecontainer body but this is wholly uneconomic. Accordingly at present itis accepted that the shelf life of beer, especially in bottles, israther limited.

It would be very desirable to be able to improve the shelf lifesignificantly whilst continuing to use conventional materials for theformation of the container body, the container closure and the gasketbetween the body and closure.

A fluid or meltable composition according to the invention is suitablefor being applied on to, and solidified on, a container closure andcomprises a polymeric matrix material, and the oxygen permeability ofthe composition (measured on a deposit formed from the composition on acontainer closure) has been reduced by incorporation of ethylene vinylalcohol polymer into the composition.

The invention includes container closures carrying a solid depositformed on the closure from such a composition and that is positioned toseal around, or over a line of weakness in, the closure.

The solid deposit can be a gasket deposited around the closure andformed from the composition. Instead of, or in addition to the depositbeing such a gasket, the deposit can (less preferably) be deposited onthe inner face of a closure at a position where there is a discontinuityor line of weakness around a push or pull component for opening acontainer sealed by the closure. The closure occupies, as isconventional, only a minor part of the exposed surface area of theclosed container, often less than 25% of the surface area. Thus the areaof the solid deposit can be very small relative to the area of thecontainer. Despite this, the invention can give greatly improved storagestability.

The invention also includes filled containers sealed with such closures.The sealed container comprises a container body, the closure fitted onit, and the filling that is contained within the container body. Thecontainer body is preferably of glass or metal. The closure ispreferably of metal.

The filling can be any beverage, foodstuff or other material that is tobe stored within the container but the invention is of particular valuewhen the filling is a material whose shelf-life is normally restricteddue to contamination, during storage, by oxygen. In particular, theinvention is of value when the filling is beer.

The container body can be a can, generally of metal, in which event theclosure is a can end. Generally the entire closure is of metal but thepanel of the closure can include a removable (generally pull) componentof polymeric material.

Preferably however the container is a jar or bottle provided with a cap.The jar or bottle can be of polymeric organic material such aspolyethylene terephthalate, polyethylene, polystyrene, polypropylene,ethylene propylene copolymer or polyacetal or a laminate including abarrier layer of an impermeable polymer but is preferably of glass. Thecap can be of polymeric organic material, for instance any materiallisted above. Preferably it is of metal but it may include a push orpull component of polymeric material.

The cap may be a crown cap, a twist-on cap or a screw-on cap, or anyother conventional form of metal cap suitable for closing the bottle orjar. If the cap and/or bottle is of polymeric material, the materialshould have very low oxygen permeability.

The invention is of particular value when the gasket is the gasket in ametal cap to a glass bottle or jar, especially the metal cap for a beerbottle.

A gasket is normally provided between the container and the closure andthis gasket is preferably formed from the composition of the inventionbut it is possible for the composition of the invention to be utilisedelsewhere on the closure in which event the gasket-forming compositioncan be any conventional composition suitable for forming the gasket.

When the closure is a cap, the gasket may be an overall gasket. Howevergenerally, for both caps and can ends, the gasket is an annular gasketand may be deposited in conventional manner from the gasket-formingcomposition. For instance an annular gasket can be formed on a can endby being applied in liquid form as an annulus around the can end and canthen be converted to solid form by drying and/or heating. Thegasket-forming composition may, for this purpose, be a dispersion,latex, plastisol, or organic solution. The can end, carrying the annulargasket, is then pressed on to an appropriate sealing face around theopen end of the filled container and folded around this face inconventional manner.

When the closure is a cap for a bottle or jar, the gasket-formingcomposition can be any of these or a plastisol, and can be applied insimilar manner, but preferably the composition is a thermoplasticcomposition. It may be applied as a low viscosity melt while the cap isspinning, so as to throw the composition into the form of an annulus, orit may be applied as a melt which is then moulded into the desiredshape, often a disc having a thickened annular portion.

It is particularly preferred, in the invention, that the gasket on thecontainer closure should be formed by applying the fluid or moltencomposition of the invention and solidifying it on the closure, themethod of application and solification generally being conventional. Itis particularly preferred that the container and can end should both beof metal or the container should be of glass and the cap of metal, sincethe use of the defined compositions for forming the gasket then appearsto give particularly beneficial results. In particular, excellentresults are achievable when the container is a glass bottle and theclosure is a metal cap, especially when the filling in the container isbeer.

Instead of or in addition to using the fluid or meltable composition ofthe invention for forming the gasket, it is possible to deposit thecomposition elsewhere on the inner face of the closure. It may beapplied as an overall coating of the inner face of the panel of theclosure or it may be applied over part only of the inner face. Inparticular, when the panel includes one or more push or pull componentsdefined in the panel by discontinuities or lines of weakness thecomposition may have been applied primarily to cover just thediscontinuity or line of weakness.

For instance one type of closure, usually a can end, includes at leastone, and often two, push components that are defined by partial scorelines through the metal panel such that finger pressure can push acircular area of the panel into the container, so as to allow access tothe contents of the container. Thus there may be a small push componentto allow release of pressure and a larger push component to allowpouring of liquid from the container. Such a system is described in, forinstance, DE 3,639,426. The fluid composition may be deposited as anannulus (or a disc) covering the line of weakness. The line of weaknessmay merely be a weakened line in the metal panel but it can be a totalcut around the push component, for instance as in DE 3,639,426, in whichevent the push component generally has an area slightly larger than theopening in the panel that is defined by the cut line and the compositionof the invention can then form a seal between the push component and theremainder of the panel of the closure.

In all instances where push or pull components are to be formed within ametal panel, there is a serious risk that the formation of the push orpull components may damage the polymeric lacquer coating that isgenerally present on the inner surface of the metal panel. This canexpose the metal to corrosion. Application of a composition of theinvention can both prevent corrosion and improve storage of fillingssuch as beer.

The composition of the invention may be formulated in any convenientfluid form, such as a melt, plastisol, organic solution, latex ordispersion. The main ingredients of the composition, apart from theoxygen scavenger, are normally typical of those conventionally presentfor the intended purpose.

The composition comprises a polymeric matrix material, that is to saypolymeric material that will form the matrix of the solidified deposit.The polymeric matrix material will be selected having regard to thenature of the composition (dispersion, latex, plastisol, solution ormelt) in conventional manner.

Suitable materials for use as the polymeric component of latexcompositions, e.g., for can ends, are described in GB 2,084,600 and EP0182674. Suitable polymeric materials for use when the compositions areorganic solutions or aqueous dispersions are described in GB 2,084,601.Suitable materials for use when the compositions are plastisols includevinyl chloride homopolymers and copolymers. Instead of preparing suchcompositions as true plastisols, they may be provided as dry blends ofthe polymer and plasticiser.

Suitable materials for use in thermoplastic compositions include thematerials proposed in GB 1,112,025 or EP 129309, 129310 or 153042. Inparticular, the polymeric material is generally selected frompolyethylene, polypropylene, ethylene propylene copolymers, butylrubber, styrene butadiene rubber, carboxylated styrene butadiene,polyisoprene, styrene isoprene styrene block copolymers, styrenebutadiene styrene block copolymers, styrene ethylene butylene styreneblock copolymers, ethylene vinyl acetate copolymers, ethylene (meth)acrylate copolymers (for instance ethylene butyl acrylate copolymers),ethylene vinyl alcohol copolymers, vinyl chloride homopolymers andcopolymers, styrene acrylic polymers, polyamides, and vinyl acetatepolymers, and blends of one or more of these.

Particularly preferred compositions according to the invention arethermoplastic compositions formed of ethylene vinyl acetate orpolyethylene or blends thereof. The polyethylene, if used, is preferablya low density polyethylene, and may be a very low density polyethylene.The ethylene vinyl acetate copolymer, if used, preferably has a meltindex in the range 1 to 15, often 3 to 15 and preferably 4 to 10.

The EVA copolymer generally contains 8 to 25%, preferably 10 to 20%,vinyl acetate. Blends of low density polyethylene with elastomers (e.g.,styrene butadiene styrene, ethylene propylene or ethylene propylenediene) may be used. The amount of elastomer typically is 5 to 25%, often10-20%, by weight of the blend.

The compositions may contain additives such as filler, slip aids,pigments, stabilisers, anti-oxidants, tackifying resins and otherconventional additives in conventional amounts, depending upon thenature of the composition. If the composition is a thermoplasticcomposition the total amount of such additives is generally below 10%,most preferably below 3%, based on the total weight of the compositionbut when the composition is a plastisol, dispersion, organic solution ordispersion the amounts of additives, based on polymeric material may behigher. For instance a large amount of filler may be incorporated.

The essential feature of the invention is that the composition fromwhich the gasket is formed contains ethylene vinyl alcohol of a type andin an amount such that the permeability of gaskets made from thecomposition is reduced. The reduction can be very significant, e.g.,usually at least 5%, often at least 10% and frequently above 15 or 20%,often as much as 50% or more of the oxygen permeability of the samecomposition but in the absence of the ethylene vinyl alcohol. Thepermeability to other contaminating vapours is also reduced.

The amount of ethylene vinyl alcohol is usually in the range 5 to 50%,based on the weight of the other polymeric components. Amounts in therange 10 to 35%, preferably 20 to 30%, are often preferred.

The ethylene vinyl alcohol polymer preferably has a melt index (in g/10min measured at 190° C., 2160 g) similar to the melt indices mentionedabove as being preferred for the other components, e.g., in the range 1to 15, often 4 to 10, most preferably 4 to 7. It typically has anethylene content of 20 to 60%, generally 30 to 50%. Preferably theethylene content is above 40%. The melting point of the polymer isgenerally in the range 150° to 180° C., preferably 160° to 170° C. Thedegree of hydrolysis of the polymer (from polyvinyl acetate) isgenerally above 95%.

The oxygen transmission rate of the polymer (measured at 35° C., dry, incc.15 μm/m².24 hrs.atm) is generally below 10 and preferably below 5.The water vapour transmission rate (measured at 40° C., 90% RH in g.30μm/m².24 hrs) is generally below 50, preferably from 10 to 40.

A composition that gives reduced permeability can usually be made bysimple melt blending of the matrix polymer and the ethylene vinylalcohol polymer, especially when the matrix polymer has a melt indexsimilar to that of the ethylene vinyl alcohol polymer. However in a fewinstances adequate reduction in permeability may not be obtained bysimple mixing. This may be due to the blend being non-homogeneous. Inthese circumstances, permeability can usually be reduced either by meltblending under increased shear or by the inclusion of a tie resin, orboth. Suitable tie resins for this purpose are materials of the typeknown for promoting bonding of polymeric films, especially a film ofethylene vinyl alcohol polymer with a film of polymeric matrix material.The amount of tie resin typically is 2 to 10%, based on the weight ofmatrix polymer. Suitable tie resins are often based on ethylene vinylacetate polymers.

By the invention it is possible to greatly prolong the shelf life of thebeer or other content of the sealed container so that the degree ofoxygen contamination of metal-capped glass bottles after, say, sixmonths is still less than the degree conventionally achieved, in theabsence of the ethylene vinyl alcohol, in less than two months. Inparticular, by the invention it is easily possible to ensure that thereis substantially no oxygen contamination of the beer for at least fourmonths after pasteurisation.

The following are some examples. In these, the oxygen permeability thatis quoted is the mean value for a layer 500 μm thick measured in cc/m²/24 hrs. All parts are parts by weight.

EXAMPLE 1

A gasket-forming composition is formed of 100 pbw matrix material and 25pbw ethylene vinyl alcohol polymer.

The matrix material is formed of 85 pbw low density polyethylene of meltindex 7.0 and 15 pbw ethylene propylene rubber of Mooney value 40 to 50(1+4 at 125° C.). The ethylene vinyl alcohol polymer has an ethylenecontent of 44%, melting point 164° C., melt index 5.5, density 1.14,oxygen transmission rate about 3 to 5 and water vapour transmission rateabout 15 to 30 (the measurement conditions and units all being asdefined above).

Oxygen permeability of the matrix material alone was 395. Thepermeability of the blend after conventional melt mixing was 190 butafter high shear mixing was 215. When 6 pbw of a tie resin was includedthe permeability was 240 by ordinary mixing or 230 by high shear mixing.This shows that typical blends of matrix material and ethylene vinylalcohol can give optimum permeability without special mixing or otheradditives.

A glass beer bottle can be sealed with a metal cap into which has beenmoulded a gasket formed from the blend formed by adding the ethylenevinyl alcohol polymer alone with ordinary mixing. The storage life ofthe beer will be found to be greatly improved compared to the shelf lifewhen the gasket does not contain ethylene vinyl alcohol.

EXAMPLE 2

The process of example 1 was repeated but using a different ethylenepropylene rubber. In this instance the permeability of the matrixmaterial alone was 400. When ethylene vinyl alcohol polymer was added byitself under high shear mixing the permeability was 230 but when it wasadded with the tie resin the permeability was 116 after ordinary mixingand 210 after high shear mixing. This demonstrates that excessive shearduring mixing can be undesirable, especially when a tie resin ispresent.

EXAMPLE 3

The process of example 1 was repeated using a dispersion of ethylenepropylene diene copolymer in high density polyethylene, instead of theethylene propylene copolymer. The permeability of the matrix materialalone was 318. After adding the ethylene vinyl alcohol polymer with highshear mixing the permeability was 195 and after adding the tie resin toit, it was 90 after ordinary mixing and 158 after high shear mixing.

EXAMPLE 4

The process of example 1 was repeated but using a styrene butadienestyrene rubber as the matrix material. The addition of the ethylenevinyl alcohol by conventional mixing caused the permeability to increaseabove its initial value of 258, but the incorporation of 6 pbw tie resincaused the permeability to drop to 127.

What is claimed:
 1. A container closure having reduced oxygenpermeability comprising a plastic closure, the closure having at leastone surface coated with a composition comprised of a polymer matrixblend formed of polyethylene, an elastomer selected from the groupconsisting of ethylene propylene copolymers, ethylene propylene dienecopolymers, butyl rubber, styrene butadiene rubber, carboxylated styrenebutadiene rubber, polyisoprenes, styrene isoprene styrene blockcopolymers, styrene butylene styrene block copolymers, styrene ethylenebutylene styrene block copolymers and blends thereof; and an ethylenevinyl alcohol polymer and wherein the composition is coated in fluid ormolten form and allowed to solidify on the surface.
 2. The closure ofclaim 1 wherein the coating is in the form of a gasket.
 3. The closureof claim 1 wherein the coating has an oxygen transmission rate (measuredat 35° C., dry, in cc.15 mm/m².24 hrs.atm) is below 10 and the watervapour transmission rate (measured at 40° C., 90% RH in g.30 mm/m².24hrs) is below
 50. 4. The closure of claim 1 wherein the oxygentransmission rate is below 5 and the water vapour transmission rate isfrom 10 to
 40. 5. The closure of claim 1 wherein the ethylene vinylalcohol polymer has a melt index (g/10 min measured at 190° C., 2160 g)in the range 1 to
 15. 6. The closure of claim 5 wherein the melt indexof the ethylene vinyl alcohol polymer and the melt index of theremainder of the components of the composition are each in the range 4to
 10. 7. The closure of claim 1 wherein the ethylene vinyl alcoholpolymer has an ethylene content of 30 to 50% and a melting point of 150°to 180° C.
 8. The closure of claim 1 further comprising about 2 to about10% by weight of a tie resin.
 9. The closure of claim 1 wherein theamount of the ethylene vinyl alcohol polymer is from 5 to 50% by weightof the other polymeric components of the composition and the reductionin oxygen permeability is at least 5%.